Ultraviolet rays cause inflammation of the skin mainly in the form of erythema, in which various chemical mediators are released to stimulate melanocytes which promote the synthesis of melanin causing the skin to darken. This darkening is caused by an excessive production of melanin in the melanocytes, then transferred to epidermic cells.
Conventionally, depigmenting cosmetics containing salts and various derivatives of vitamin C, hydroquinone monobenzyl ether, hydrogen peroxide or the like have been proposed to prevent pigment deposition, spots, freckles or the like on the skin and to maintain natural white skin. Further, various plant extracts or plant-derived materials such as gallic acid and geranial or the like have been proposed for use in such cosmetics. Furthermore, hydroquinone or hydrochalcone derivatives such as phlorine, phlorizin, phlorezin (Japanese Patent Laid-open 92/235112), dihydrophloretin (WO95/11662) have been reported to have an effect in suppressing the synthesis of melanin.
However, most of these compounds were found not to be very effective in preventing pigment deposition or in depigmenting the skin because of their poor shelf life when formulated, or their poor efficacy in suppressing inflammation caused by ultraviolet irradiation. Further, when hydroquinone monobenzyl ether or the like are combined in such cosmetics, although skin darkened with deposited pigment can be effectively lightened, there are side effects such as skin allergies and irritation or other problems. Furthermore, the various plant extracts have problems, such that their efficacy is not quite satisfactory, or the quality of the extracts is not always consistent.
Furthermore, although it has been reported in U.S. Pat. No. 4,954,659 that hydrochalcone compounds have anti-oxidative activity, their potential usefulness in cosmetics has not been disclosed.
Thus, it is very difficult to obtain cosmetics which are highly effective in suppressing pigment deposition and depigmentation and which are very safe to the skin and have good shelf life. Therefore, development of cosmetics satisfying these was desirous.